Current tube-launched, optically-tracked, wire-guided (TOW) missiles are tracked using technology developed in the 1960s. Historically, TOW missile trackers use only two elements configured in an L-shaped pattern with a lens in front that nutates scene images in a circular pattern across the detectors. A xenon beacon on the rear of the TOW missile is modulated at a much higher frequency than the nutation frequency of the tracker, which, by temporal frequency filtering, allows the beacon to be separated from background clutter on the detector. The relative phase or angle of the nutation circle of the beacon as it crosses each detector relative to a reference signal allows the determination of the azimuth and elevation position of the beacon. The azimuth and elevation signals are then provided to guidance algorithms to steer the missile to the desired target.
The basic tracking technology described above is still in use in all of U.S. inventory TOW missile systems. Despite the accuracy of the TOW missile, the technology is also prone to jamming when the modulation frequency of the beacon is known. The only current workaround to xenon jamming or multiple missiles in the field-of-view of the missile tracker is the use of the TOW II missile, where an additional forward looking infrared (FLIR) tracker and infrared beacon is utilized in conjunction with the xenon beacon tracker.
In the mid-1990s, a number of xenon beacon wire-guided European missiles began conversion to using CCD imaging based trackers also known as CCD localizers. Imaging trackers have the advantage of a natural resistance to jamming once tracking has been initiated due to the fact that there is spatial separation between the signal being tracked and the jamming signal. These imaging trackers use a single CCD array and a single or dual field-of-view (FOV) lens to image the xenon beacon onto the array. Some variance may synchronize the imager frame rate to the high frequency of the xenon modulation (e.g., greater than one kilohertz) or operate at a very high frame rate near the modulation frequency of the xenon beacon.
The use of single focal plane array (FPA) imaging solutions that have been used heretofore have disadvantages that are difficult to overcome. First, the use of a single FPA must either be synchronized to the xenon beacon pulse rate in order to differentiate the xenon beacon from background clutter or the single FPA must operate at a very high frame rate (i.e., greater than one kilohertz) in order to detect the modulation frequency of the xenon beacon in order to identify the beacon from background clutter. Since current U.S. TOW missiles operate in a completely open-loop form with the xenon beacon, there is no signal available without a complete redesign of the missile itself to allow for synchronizing the single FPA. Also, very high angular resolution for azimuth and elevation determination of the beacon necessitates large format focal plane arrays, where greater than one mega pixels is preferable. However, these FPAs are not conducive to high frame rates, which makes the use of a single FPA solution difficult to use for tracking TOW missile beacons.